Various techniques for molding hollow plastic articles and containers are known in the prior art. By one of these techniques, multiwalled containers may be produced by an injection blow molding procedure. Such a container may, for example, incorporate an inner wall or layer comprised of a thermoplastic resin having barrier properties (e.g. as respects water vapor or carbon dioxide transmission) and an outer wall or layer comprised of a thermoplastic resin having structural properties. In accordance with one such technique, a preformed liner of thermoplastic material which can, for example, be comprised of two or more layers or walls of differing thermoplastic resins is positioned over a core rod. The core rod is then positioned in the cavity of an injection molding zone and an injectable heated thermoplastic resin is injected into such cavity to form a composite preform or parison wherein the liner comprises the liner wall portion thereof. The composite preform on the core rod is removed from such injection mold cavity and is positioned next in the cavity of a blow molding zone. Fluid pressure is exerted on the preform between the preform and the core rod to an extent sufficient to make the preform expand into contact with adjacent wall portions defining the blow mold cavity which results in the production of a blown container. The blown container is removed from the blow mold cavity and the blown container is then separated from the core rod.
In endeavoring to practice such one technique at commercially acceptable rates so as to produce commercially acceptable product containers, problems have been experienced because of a tendency for the liner to experience creasing during formation of the preform apparently due to a variety of factors many of which appear to be associated with orientation and/or liner size variations in relation to an adjacent core rod. In practice such creasing tendency results in a significant percentage of product containers being formed of substandard quality.
Because of price and cost considerations, it is necessary for commercial purposes to have little or no rejects in a plastic manufacturing operation. Hence, in order to produce by such one technique high quality containers at commercial rates with few rejects, it is necessary to have an improvement in the practice of such one technique.